Stocks ended flat after a choppy trading session, amid a sharp sell-off in Hewlett-Packard and renewed worries about Europe as European finance ministers met to discuss the latest release of bailout funds for Greece. Housing starts rose to the highest level in four years, but housing permits declined slightly to an annual rate of 866,000 last month, less than the 870,000 expected. Best Buy dropped 13% after the co. reported disappointing earnings and sales and cut its full-year outlook. Hewlett-Packard tumbled 11.9% after the co. said it would take a massive charge related to its controversial acquisition of Autonomy. Advancers included Groupon which gained 8.5% after late Monday, hedge fund Tiger Global disclosed it had acquired a 9.9% stake in Groupon. In the evening trade Salesforce rose as much as 2% after hours as the firm topped Wall Street estimates and raised its outlook for 2013. Implied volatility inched higher on moderate trading volumes.